Hydraulic lift truck



Nov. 15, 1949 D. c. WALMSLEY 2,488,356

HYDRAULIC LIFT PRUCK Filed May 10, 1945 2 Sheets-Sheet 1 Nov. 15, 1949 D. c. WA'LMSLEY HYDRAULIC LIFT TRUCK 2 Sheets-Sheet 2 Filed May 10, 1945 6 M f m m T 0 mm 7 W M w M fi Patented Nov. 15, 1949 HYDRAULIC LIFT TRUCK David C. Walmsley, Battle Creek, Mich, assignor to Schwitzer-Cummins Company, Indianapolis,

Ind., a corporation Application May 10, 1945, Serial No. 593,069

3 Claims. 1

This invention relates to a lift truck, particularly that type employed in shops to roll under a load carrying skid to lift and transport it. It is more particularly directed to a power driven truck provided with hydraulically actuated lift mechanism.

The principal feature of the invention resides in the new and novel lift mechanism for a truck, and particularly wherein said mechanism is carried by a supporting frame of fixed level. Thus, the invention contemplates connecting the lift platform with a fixed platform through the medium of a bell crank lever supporting it at one end, and wherein a trunnion supports it at the other end upon the axle of a pair of rear wheels. The actuating means such as a hydraulically operated piston is provided for swinging the bell crank lever and trunnion through a draw bar to simultaneously displace the lift platform upwardly and toward the fixed frame I through a parallelogram movement including swinging the supporting wheels from retracted to lift position.

The full nature of the invention will be understood from the accompanying drawings and the following description and claims:

Fig. 1 is a plan view showing the frame structure of the truck.

c Fig. 2 is a central vertical section showing the lift platform in lowered position.

Fig. 3 is the same as Fig. 2 showing it in elevated position.

In the drawings there is illustrated a lift truck having a supporting frame l0 and a lift platform frame II, the latter being displaceable relative to the supporting frame. The supporting frame [0 is supported at a fixed level by the wheels l2 and a front driving wheel 13 upon which the frame I0 is supported by the overhanging supporting frame bars M, as illustrated and dedescribed in the application of Schwitzer and Roland filed December 11, 1943, Serial No. 513,858, now Patent No. 2,443,480 dated June 15, 1948, entitled Power driven vehicle. However, the power driving mechanism for the front driving wheel l3 and the mounting of the supporting frame thereon, as shown in the above application, forms no part of this invention, since it is immaterial here as to the means for propelling the truck, either by power or by hand. The supporting frame Ill carries a platform upon which the operator may stand for operating the truck if it is power driven, and mounted upon the frame or the platform there is a double acting hydraulic hand pump indicated at I 5, which 55 Y 2 pump is shown and described in my copending application filed April 20, 1945, Serial No. 589,317, entitled Pump.

The frame ll of the lift platform may carry a platform bed I6. The forward end of the frame H of the lift platform is provided with an underslung extension frame I! which extends forwardly under the supporting frame ID with its forward end pivotally supported at 18 by a lift arm 1 9 having its upper end pivoted at 20 within a bearing 2| secured to the underside of the supporting frame. Said lift arm is in the form of a bell crank lever, as indicated at 22, having its rear portion provided with a socket 23 to which a draw bar 24 is connected at one end.

As shown in Fig. 1, there is a pair of such bell crank levers and sockets to which a pair of said draw bars is connected.

Said draw bars extend under the lift platform to the rear thereof, having pivotal connection at their opposite end with the rear axle 25 of the lift platform on which the rear supporting wheels 26 are carried. The axle 25 extends through and is supportedby an axle housing 2'! which supports and carries most of the load, but is normally mounted relative to the frame II and connected thereto by a trunnion 28 acting as a rear lift arm. The trunnion carries the axle housing 21 and is pivotally supported upon a cross bar 29 extending across the frame I I and secured thereto at opposite ends. This arrangement is such that the rear supporting wheels 26 of the lift platform may be swung from retracted position, as shown in Fig, 2, forwardly to elevating position, as shown in Fig. 3, by the forward movement of the draw bars 24. This swinging movement of the wheels 26 disclose the lift platform to elevate it when in forward position and lower it when in retracted position.

For actuating the bell crank levers 22 and draw bars, there is provided a hydraulic cylinder 30 having fluid connection with the hydraulic pump [5. Said cylinder is pivotally supported at 3| to the underside of the supporting frame It). The piston rod 32 of said cylinder extends forwardly and slightly downwardly therefrom for pivotal connection at 33 with the bell crank lever 22. Upon the cylinder 30 being hydraulically actuated to force the piston rod 32 forwardly, it swings the bell crank lever with its lift arm 19 forwardly and upwardly from the position shown in Fig. 2 to the position shown in Fig. 3. This movement has the effect of raising the pivotal mounting [8 of the extension frame ll forwardly and upwardly, such as to elevate fthefront end of the lift platform. At the same 1 time, it moves the draw bars forwardly to swing the rear wheels 26 from retracted position to elevating position, such as to elevate the rear end of the lift platform. Thus, the lift platform is displaced upwardly and toward the supporting frame ill with a parallelogram movement such as to atall times maintain the platform in level position. 'For this purpose when in lowered position there is a sufiicient gap between the forward end of the lift platform and;

the supporting frame to permit of its displacementand relative movement therebetween.

The forward portion of the bell crank lever or the under portion of the lift arm l9 is provided with a lip 34 positioned to be en aged by a latch 35 which is releasable by a foot treadle 36 operatively connected with the latch'to swing it outwardly to unlatching position about itspivotal mounting 31 on the supporting frame It).

- Whereas the .inventionis shown herein aslbe ing actuated hydraulically through the medium of the pump and cylinder 30, amechanical or carried by the rear wheels and axlehousing 2.1

through; the vertically positioned trunnion or lift arm 28 when in elevated position. This takes most of the load off of the hydraulic cylinder 3i! atthe front end. Also, when in lowered position the frame H .rests directly on thehousing 21 which then provides afixed support therefor.

' The invention claimed is:

] 1. A lift truck including a supporting frame having wheels for carrying it at a fixed level, .a lift platformv connected with displaceable relative thereto, a bell crank lever pivota1ly supported at one end to the.underside ofsaid frame, an underslung extension frame extending from thehfree end of said platform and terminating under said supporting frame and havinga pivotal connection with said bell crank lever, a pair of rear supporting wheels for theopposite end-of said lift platform, a'trunnion pivotally connected to; the axle of said wheels at one end and to the underside of said lift platform at the other end thereof to swing'ably support said platform on said wheels, a pair of draw bars intercom. necting the axle of said wheels with said .bell

cranklever, the bell crank lever and trunnion,

both swinging in one direction for platform elevation and both swingingin the opposite direction for platform lowering .and means carried by said supporting frame and connected with said-bell crank lever and operable to displace said. ball crank lever relative to said supporting frame to raise the forward end of said lift platform therewith and move the rear supporting wheels forwardly to platform elevating position.

2. A lift truck including a supporting frame having wheels for carrying it at a fixed level, a lift platform connected with and displaceable relative thereto, a bell crank lever pivotally supported at one end to the underside of said frame, an underslung extension frame extending from the .free end of said platform undersaid supporting frame having a pivotal connection with said bell crank lever, a pair of rear supporting wheels for the opposite end of said lift platform, a trunnionpivotally connected to the axle of said wheels at one end and to the underside of said lift platform at the other end thereof to swingably support'said platform on said wheels, a pair of draw bars interconnecting the axle of said wheels with saidbell crank lever, means carried by said supporting .frame connected with said bell crank lever operable to displace said bell crank lever relative to said supporting frame to raise the forward end of said lift platform therewith and move the rear supporting wheels forwardly to platform elevating position, and a'manually controlled latchmounted on said frame for latching engagement with one free swinging end 'ofsaid lever When the lever is in displaced positionvto lock it in platform elevating position.

3; A lift truck including a supporting frame havingwheels for carrying it at a fixed level, a lift platform connected therewith and displace able relative thereto, abell crank lever'pivotally supported at one end to the underside of said frame, an underslung extension frame extending from the free end of said platform under said supporting frame having a pivotal connection with said bell crank lever, a pair of rear support.- ing wheels for the opposite end of'said liftplatform, a trunnion pivotally connected "to the axle of'said wheelsat one end and to the underside of said liftplatform at the other end thereof to swingably support said'platform on saidwheels, a pair of draw bars interconnectingthe'axle, of said wheels with said bell crank lever, ahydraulioally actuated piston and cylinder connected between said frame and lever, and a hydraulic pump carried by said truck'for actuating said piston and cylinder for moving saidlever, bars and wheelsto and from platform elevating position;

-DAVIDIC. WALMSLEiY."

REFERENCES CITED The following references are of record in the file of this patent:w

UNITED STATES PATENTS 

